1. Field of the Invention
The present invention relates to a frequency synthesizing apparatus for a multi-band radio frequency (RF) receiver, and more particularly, to a multi-input multi-frequency synthesizing apparatus and method which can reduce a circuit area and may be low powered.
2. Description of Related Art
A high speed wireless data transceiving system such as a cellular phone, a digital multimedia broadcasting (DMB) phone, a personal digital assistant (PDA), etc., needs a frequency synthesizer or a frequency mixer processing multi-tones for frequency down conversion in a transceiver. As an example, a multi-frequency synthesizer is utilized to receive a radio frequency (RF) signal and convert the received RF signal into a baseband signal, in a Code Division Multiple Access (CDMA) system, a global positioning system (GPS), a personal communication system (PCS), an International Mobile Telecommunication (IMT)-2000 system, Wireless Broadband Internet (WiBro) system, a wireless local area network (WLAN) system, an Ultra Wideband (UWB) system, and WiMax system for a ubiquitous system.
FIG. 1 is a diagram illustrating a single side band (SSB) mixer 100 according to the conventional art. Referring to FIG. 1, the SSB mixer 100 includes a first double side band (DSB) mixer 110, a second DSB mixer 120 and an adder/subtractor 130.
Each of the first DSB mixer 110 and the second DSB mixer outputs a DSB signal simultaneously mixed with a component which is an addition of frequencies of two received signals and another component which is a difference of frequencies therebetween. Namely, the first DSB mixer 110 outputs a DSB signal mixed with both a component which is an addition of frequencies of a first high frequency signal RF1I and a second high frequency signal RF2I and a component which is a difference of frequencies therebetween. The second DSB mixer 120 outputs a DSB signal mixed with both a component, which is an addition of frequencies of a Q signal, RF1Q, of the first high frequency signal RF1I and a Q signal, RF2Q, of the second high frequency signal RF2I, and a component which is a difference of frequencies of the two Q signals. In this instance, a Q signal is a quadrature signal having a 90 degree phase difference. Accordingly, when outputs of the first DSB mixer 110 and the second DSB mixer 120 pass through the adder/subtractor 130, an SSB signal LOM or an SSB signal LOD may be outputted. In this instance, the SSB signal LOM is a signal whose frequency is an addition of frequencies of the first high frequency signal RF1I and the second frequency signal RF2I, and the SSB signal LOD is a signal whose frequency is a difference of frequencies therebetween.
As described above, a single SSB mixer can only generate two components which are an addition of frequencies of two received signals or a difference of frequencies therebetween. Accordingly, a plurality of SSB mixers and switches are generally utilized for processing a multi-band in a ubiquitous system.
FIG. 2 is a diagram illustrating a frequency synthesizer 200 for generating multi-tones according to the conventional art. Referring to FIG. 2, a plurality of SSB mixers 230 are utilized for supplying a corresponding local signal LO to a receiver (Rx) mixer. In this instance, the Rx mixer down converts a multi-band RF signal received from an RF receiver to a baseband. The plurality of SSB mixers 230 receive high frequency signals, RF1, RF2, . . . , from a voltage controlled oscillator (VCO)/frequency divider (DIV) 220, which are connected to a phase locked loop (PLL) 210, and synthesize a necessary frequency signal. In this instance, a plurality of PLLs, VCOs or DIVs may be utilized. Also, switches are needed for selecting any one of multi-frequency signals synthesized in the SSB mixers 230, which is necessary for down-converting a received RF signal. As an example, when high frequency signals in an n number of bands are generated by using the VCO/DIV 220, 2n of frequency signals may be generated by using 2n−1 of SSB mixers 230.
As described above, necessary multi-band signals may be generated by using a large number of SSB mixers. However, in this case, a required circuit area may be unacceptably increased to accommodate a PLL, a VCO/DIV and SSB mixers, and a large amount of power may also be consumed.